This invention relates to a modified polyetherimide especially suitable for injection molding. Polyetherimides are unique polymers which exhibit superior strength and chemical properties, including high heat resistance, exceptional strength, and excellent processibility.
It is known that injection molded articles can be produced from polyetherimides. However, notwithstanding excellent mechanical properties, resistance to chemical attack, and processibility, delicate parts have a tendency to stick to the mold during injection molding. When these intricate parts, i.e., 10 mils, are ejected from the molds, many break. Another problem faced in the injection molding of intricate parts made from polyetherimides is the inability to fill the fine cavities of the mold.
Many injection molding resins such as polyesters, are known to stick to the molds. Generally, conventional mold release agents have been used successfully for the elimination of this problem. Such conventional mold release agents include metallic salts and esters of fatty acids, typically stearic acid. While these mold release agents have proven successful for many polymers, unfortunately they tend to decompose at the high processing temperatures used for polyetherimides.
Excellent lubricants such as silicones or Teflon.RTM. sprays are known mold release agents. External lubricants are disadvantageous in that they introduce additional process steps in the molding operation and can cause surface contamination of the molded article.
Therefore, there exists a need for a polyetherimide resin that can be injection molded efficiently with reduced sticking to the mold.